I'll take a guess that losing one barrel is barely noticeable, losing two gives a bit of slop but probably isn't that bad (especially if like mine a chunk of it wedges in the gap between the outer and inner parts of the Centa) but when the third barrel goes it will all get messy and the fourth one won't stand a chance with lots of slop until the debris wedges in the corners to transmit some drive.
The rubber barrels are at least cheap, it's the hours of work to get at them that is the problem. Best of luck with it.

Calum
M3W Vol1
Vol2